The present invention relates to a radiation exposure dose-history indicator, which can display the radiation dose applied to, for instance, medical appliances and the blood for transfusion, by means of the developed or changed color thereof, which permits the distinctive recognition of the color changes and which never undergoes any color deterioration or discoloration.
The radiation exposure treatments such as the application of, for instance, X-rays or xcex3-rays have in general been used for the sterilization of medical appliances and these treatments have recently been applied to the blood for transfusion in order to prevent any crisis of graft-versus-host diseases (TA-GVHD) due to the blood for transfusion. The radiation exposure dose applied to the blood for transfusion is not more than 1/100 times the radiation dose required for the radioactive sterilization of medical appliances and thus it reasonably ranges from 15 to 50 Gy (1,500 to 5,000 rad).
In general, to examine whether a desired radiation dose is applied to a subject to be irradiated therewith or not, radioactive rays are applied to the subject in the coexistence of an indicator including a substance, which undergoes an irreversible color change upon exposure to the rays, and after the radiation exposure, the indicator is withdrawn from the subject to confirm the color change thereof. As an example of such an indicator for the radioactive sterilization of medical appliances, those each comprising a combination of a dye susceptible to acids and polyvinyl chloride have already been put into practical use. This indicator undergoes a color change when the radiation exposure dose is not less than 5,000 to 25,000 Gy, but it never causes any color change at a radiation exposure dose level of not more than 50 Gy, which corresponds to that required for the application of radioactive rays to the blood for transfusion.
As substances, which undergo color changes at a radiation exposure dose level of 15 to 50 Gy, there have been known, for instance, inorganic crystalline substances, each of which comprises an alkaline halide of potassium chloride or the like doped with calcium. However, it is quite difficult to confirm the color change of this crystalline substance, to change its shape to those other than crystalline ones and to process the crystals. Moreover, Japanese Patent Application Publication No. Hei 7-18924 discloses an indicator, which makes use of the polymerization reaction of a polyacetylene compound upon exposure to radioactive rays. However, this polymerization reaction may proceed by the action of not only the radioactive rays, but also a heat. In other words, this indicator requires the storage at a low temperature condition and it also causes an indistinct color change due to the polymerization reaction.
These conventional indicators suffer from such a problem that they undergo insufficient color changes and this in turn leads to the misjudge of the result, since in case of the conventional indicators, whether the radiation exposure dose is reasonable or not is confirmed on the basis of color changes thereof, when subjecting a radiation exposure treatment to, for instance, the blood for transfusion.
The present invention has been developed to solve the foregoing problems associated with the conventional indicators for the quantification of the radiation exposure dose and accordingly, it is an object of the present invention to provide a composition used in an indicator, which can easily and accurately display the radiation exposure dose by means of the clear change in its color hue and which does not cause any color deterioration even if it is stored over a long period of time, as well as an indicator sheet prepared using the same.
The composition for a radiation exposure dose-history indicator according to the present invention, developed for achieving the foregoing object, comprises a radioactive ray-absorber and/or a radioactive ray-excited fluorescence-emitting agent, a color-developing and electron-donating organic compound and an active species-generating organic compound, which can induce the color development of the electron-donating organic compound through the application of radioactive rays. The composition may further comprise a hydrophilic compound.
The indicator sheet for indicating the radiation exposure dose-history comprises a base sheet 2; and a color-developing layer 1 containing a color-developing and electron-donating organic compound, an active species-generating organic compound which can induce the color development of the electron-donating organic compound through the application of radioactive rays, and a radioactive ray-absorber and/or a radioactive ray-excited fluorescence-emitting agent, the layer 1 being applied to at least part of the surface of the base sheet 2. The color-developing layer may further comprise a hydrophilic compound.